Regulation of irrigation water

ABSTRACT

A method for improving the irrigation of highly permeable surface soils is described wherein the soils are contacted with an effective amount of an aqueous solution of a partially hydrolyzed polyacrylamide to reduce the water permeability of the soil without rendering the soil impermeable to waterflow. The invention has application for irrigation of sandy and highly permeable soils which experience a rapid loss of water from the root zone following irrigation by drainage or percolation, as well as rapid evaporation and drying by movement of the water to the surface. The soils are contacted with a solution having a concentration of about 0.0001 to about 1 weight percent of a polyacrylamide having from 5 to about 80 percent of its amide groups hydrolyzed to carboxylic acid groups. This treatment is performed periodically or annually so as to reduce the permeability of the soil to subsequent irrigation waters.

United States Patent 72] Inventor Burton B. Sandiford Placentia, Calif.[21] App1.No. 853,531

[22] Filed Aug. 27, 1969 [45] Patented Jan. 11, 1972 [73] .AssigneeUnion Oil Company Los Angeles, Calif.

[54] REGULATION OF IRRIGATION WATER 7 Claims, No Drawings [52] US. Cl47/58, 61/36, 260/41,47/DIG. 10 [51] Int. Cl E02d 3/12 [50] Field ofSearch. 47/9, 58,

DIG. 10; 61/36; 260/37,41

3,118,832 1/1964 Katzer et a1 61/36 X 3,268,002 8/1966 Fischer 61/36 XFOREIGN PATENTS 788,677 1/1958 Great Britain 47/D1G. 10

Primary Examiner- Robert E. Bagwill Attorneys-Milton W. Lee, Richard C.Hartman, Lannas S.

Henderson, Dean Sandford and Robert E. Strauss ABSTRACT: A method forimproving the irrigation of highly permeable surface soils is describedwherein the soils are contacted with an effective amount of an aqueoussolution of a partially hydrolyzed polyacrylamide to reduce the waterpermeability of-the soil without rendering the soil impermeable towaterflow. The invention has application for irrigation of sandy andhighly permeable soils which experience a rapid loss of water from theroot zone following irrigation by drainage or percolation, as well asrapid evaporation and drying by movement of the water to the surface.The soils are contacted with a solution having a concentration of about0.0001 to about 1 weight percent of a polyacrylamide having from 5 toabout 80 percent of its amide groups hydrolyzed to carboxylic acidgroups. This treatment is performed periodically or annually so as toreduce the permeability of the soil to subsequent irrigation waters.

REGULATION OF IRRIGATION WATER DESCRIPTION OF THE INVENTION Thisinvention relates to a treatment of agricultural soils and in particularrelates to a treatment of highly permeable surface soils to reduce thewater permeability of the soils and thereby reduce loss of water fromthe root zone.

Sandy and highly water permeable soils are frequently encountered in thepractice of irrigation since many of these soils have been reclaimed byirrigation from arid and semidesert areas. Irrigation of these soilsfrequently results in a rapid loss of water by percolation of water awayfrom the root zone. ln addition, the soils have a tendency to rapidlydry by evaporation since the moisture in the soil readily moves to thesurface from which it is evaporated. This rapid drying of the highlypermeable soils results in a requirement that the soils be irrigatedmore frequently than desirable.

It is an object of this invention to provide a method for treatment ofsurface soils to reduce the permeability of water therethrough.

It is likewise an object of this invention to provide the method for theirrigation of such soils.

Other and related objectives will be apparent from the followingparagraphs.

have now found that the aforementioned objectives can be achieved by thecontacting of the soils with an effective amount of an aqueous solutionof a partially hydrolyzed polyacrylamide to reduce the waterpermeability of the soil without rendering the soil impermeable towaterflow. The contacting of the soil can be performed periodically bythe addition of a small amount of the aforementioned partiallyhydrolyzed polyacrylamide to the irrigation water supplied to the soil.Thereafter, conventional irrigation practice is followed by theapplication of water to the soil when necessary to maintain the watercontent of the soil above the minimum amount corresponding to thepermanent wilting value. The soil can be contacted with the solution ofthe partially hydrolyzed polyacrylamide frequently during the irrigatingseason or, the treatment can be applied annually or semiannually. Thenecessity for the application of the treatment can be readily determinedby taking test cores of the surface soil, i.e., the upper 6 to upper l8inches, and measuring the rate of waterflow through the test core. Thenecessity for retreatment of the soil can also be determined byobserving the frequency by which the soil requires irrigation and whenthe period between irrigations is substantially reduced from thatimmediately following the polymer treatment, the soil is again necessaryfor retreatment by contacting with the aqueous solution of the partiallyhydrolyzed polyacrylamide.

The polymer useful in the invention comprises a partially hydrolyzedpolyacrylamide which is obtained by the polymerization, preferablyhomopolymerization, of acrylamide. If desired, however, up to about 10weight percent of other vinyl monomers such as vinyl acetate,acrylonitrile, methyacrylonitrile, vinyl alkyl ethers, vinyl chlorideand the like can be employed, provided that the copolymers so obtainedare characterized by water solubility and freedom from crosslinking. Theacrylamide is polymerized by suitable vinyl polymerization initiators,e.g., free radical forming compounds such as the azo compounds, e.g.,azobisisobutyronitrile, azobisisobutyro-amidine chloride, etc.;peroxides such as hydrogen peroxide, sodium peroxide, benzoyl peroxide,alkyl peroxides such as t-butyl hydrogen peroxides; and dialkylperoxides such as diethylperoxides, di-t-butyl peroxide, etc.; alkalimetal persulfates, etc.

These polymers are characterized by high-molecular weight, e.g., 300,000to about l5,000,000, preferably from about 500,000 to about 5,000,000.The viscosity of aqueous solutions of the polymers are reflective .ofthe molecular weight of the polymers, higher molecular weight polymersimparting greater viscosities at the same concentrations than that ofthe lower molecular weight polymers. Accordingly, the minimum molecularweight for the polymers used in this invention is sufficient that a 0.5weight percent aqueous solution of the polymer has a viscosity of atleast about 6 centipoises at 25 C. as determined in a standard Ostwaldviscosimeter.

For use in the invention, the polyacrylamide polymers are partiallyhydrolyzed to the extent that from 5 to about 80, preferably from about7 to about 65, and most preferably from about 12 to about 45 percent ofthe amide groups of the polymer are hydrolyzed to carboxylic acid orwater soluble carboxylate groups. The resultant acid groups can bepresent as the carboxylic acid or as water-soluble carboxylates such asthe ammonium, alkali metal and alkaline earth metal salts thereof, e.g.,sodium, potassium, cesium, lithium, calcium, magnesium, etc.

The hydrolysis of the polyacrylamide can be performed after thepreparation of the polymer by prolonged exposure of an aqueous solutionof the polymer to elevated temperatures and pH in the presence of alkalimetal hydroxides or carbonates. It is similarly possible to prepare thepartially hydrolyzed polyacrylamide by a step of simultaneouslypolymerizing and hydrolyzing the resultant polymer. Such a method isdescribed in U.S. Pat. No. 3,022,279 wherein an aqueous solutioncontaining at least about 5 percent by weight of acrylamide, a freeradical polymerization initiator and sodium carbonate at a concentrationof from 10 to 67 molar percent of the acrylamide are heated to atemperature from about 20 to 55 C. to initiate the polymerization andsimultaneously polymerize and hydrolyze the polymer to the desiredpartially hydrolyzed composition. Another technique for the simultaneouspolymerization and hydrolysis of the polymer comprises performing thepolymerization with an aqueous solution containing at least about 5percent acrylamide and an alkali metal polyphosphate in an amount fromabout 5 to 25 molar percent based on the acrylamide using a free radicalcatalyst initiator and a temperature from about 25 to C. to initiate thepolymerization while retaining the resultant solution at the elevatedtemperature for a sufficient time to hydrolyze from 5 to about 80percent of the amide groups to the carboxylic or carboxylate groups. Thenecessary time to effect the hydrolysis whether it is performedconcurrently with or after the polymerization of the acrylamide is fromabout 5 to about 20 hours, preferably from about 8 to about l2 hours,and is sufficient to effect the aforementioned partial hydrolysis of theacrylamide groups. The partially hydrolyzed polymers are alsocommercially available as dried powders under the trade designations ofSeparan NP20, Pusher 500 or 700, BT60], from the Dow Chemical Company.

The partially hydrolyzed polyacrylamide is employed in an aqueoussolution which contains from about 0.001 to about 1 weight percent ofthe polymer. At this concentration the polymer will exhibit a viscosityfrom 2 to about 1,000 centipoises. Preferably the concentration isadjusted to provide a solution having a viscosity from about 5 tocentipoises. The polymer can be dissolved in ordinary irrigation waterby simple admixing of the polymer with the irrigation water, orpreferably, the polymer is dissolved in an aqueous concentrate having aconcentration from about 0.5 to about 2.0 weight percent of the polymerand thereafter this concentrate can be blended into the irrigation waterin a sufficient quantity to provide the aforementioned desiredconcentration of the polymer in the solution which is contacted with thesurface soil.

The contacting of the surface soil with the solution containing thepartially hydrolyzed polyacrylamide need only be performed periodically,whenever the permeability of the soil has increased to an undesirablelevel as reflected by the greater frequency for irrigation necessary tomaintain soil moisture above a permanent wilting value or as determinedby obtaining a core of the surface soil and measuring the permeabilityof waterflow therethrough. The partially hydrolyzed polyacrylamidepolymers are quite stable in soils, however, after prolonged periodssome of the polymer can be removed from the soil by washing and/orbacterial action. Accordingly, it is necessary to periodically retreatthe soil and this retreatment can be as infrequently as once each yearor each growing season or can be made after each cultivation of thesoil.

The amount of the treating solution can be varied as necessary to effectthe desired reduction in permeability of the soil. Generally this amountcan comprise from 0.05 to about 5 volumes of solution per pore volume ofthe soil, preferably from about 0.1 to about 2 volumes per pore volume.The treatment is applied to the soil surrounding the root zone of theparticular crop, e.g., the upper 18 inches, preferably the upper 6inches of the soil surface is treated with the solution. The degree ofpenetration of the treating solution can be readily controlled by theamount of solution applied during a single treatment.

The necessity for irrigation can be determined as in the conventionalpractice, e.g., by the use of field instruments for the determination ofthe soil moisture content as reflected by the soil suction pressurewhich ranges from about 0.85 to 15 bars, the l5-bar value reflecting thepermanent wilting point of most soils. An electrode-type resistance unitsuitable for measurement of soil moisture content independently of thephysical characteristics of the soil is described in Soil Science,Volume 97, pages 108-1 12.

The invention will now be described by reference to the followingexample which demonstrates the results obtainable thereby:

EXAMPLE 1 A laboratory test core of a Nevada No. 130 sand, 1 inchdiameter and.3 inches in length, was prepared. The pore volume of thesand core comprised 15 milliliters. The sand was unconsolidated in thecore sample and water readily permeated therethrough. The test core wasconnected to water supply means with facilities to measure the rate ofwaterflow therethrough under a hydrostatic head of 6 inches water. Underthese conditions it was observed that the waterflow rate through thesand core was 10 milliliters in 5 minutes, 7 seconds. An aqueoussolution of partially hydrolyzed polyacrylamide designated as Pusher 700was dissolved in water at a concentration of 0.2 weight percent. Thesolution had a viscosity of 98 centipoises when measured at 6 r.p.m. ona bland viscosimeter and 74.4 centipoises when determined at 12 r.p.m.on the viscosimeter. The aqueous solution was contacted with the sandcore under a hydrostatic head of 21 inches of water and a rate of flowthrough the said core comprises l milliliters over a period of 180minutes, seconds. Thereafter irrigating water was again supplied to thecore under a hydrostatic head of 6 inches of water and passed throughthe core for a period 6 hours, until the previous aqueous solution ofthe partially hydrolyzed polyacrylamide had been thoroughly displacedfrom the core. Thereafter, the rate of flow of the water through thesand core was measured and the following flow rates were determined atthe hydrostatic head of 6 inches water:

Cumulative Volume of Water Flow Rate of Flow 75 milliliters 10 ml. in 28min/32sec. milliliters 10 ml. in H5 min/54 sec. milliliters I0 ml. in 26min/8 sec. 325 milliliters 10 ml. in 32 min./37 sec.

The above data illustrate that the sand core exhibited a permanentlyreduced permeability to waterflow. The quantity of water passed throughthe sand core after the aqueous solution had been thoroughly washed fromthe sands was the equivalent of about 25 inches of water orapproximately 2 acre feet of water per acre, corresponding to the amounttypically used in semiarid areas during a growing season.

The aforementioned example is intended solely to demonstrate the resultsobtainable by my invention. It is obvious that my invention can bepracticed in accordance with the procedure set forth in theaforementioned specification and that modifications of use employingObVlOUS equivalents can be used without departing from the scope of theinvention.

1 claim:

1. The method of irrigating highly water-permeable surface soils toreduce the quantity of irrigation water required for plant growth whichcomprises: (i) contacting said soil with an effective amount of anaqueous solution of a partially hydrolyzed polyacrylamide having a molweight from 300,000 to 15,000,000, sufficient to provide a 0.5 weightpercent aqueous solution thereof with a viscosity of at least 6centipoises at 25 C. and having from 5 to about 80 percent of its amidegroups hydrolyzed to carboxylic acid groups to reduce the waterpermeability of said soil without rendering said soil impermeable towater flow; and (2) thereafter irrigating said soil with water havingnone of said polyacrylamide at periodic intervals as required tomaintain the water content of the soil above the amount corresponding tothe permanent wilting value.

2. The method of claim 1 wherein said aqueous solution contains from0.001 to l .0 weight percent of said polymer.

3. The method of claim 2 wherein said polymer has from 12 to 45 percentof its amide groups hydrolyzed to carboxyl groups.

4. The method of claim 2 wherein said treating solution is applied tosaid soil in an amount from 0.05 to about 5 volumes of solution per porevolume of said soil.

5. The method of claim 2 wherein said treating solution is applied tosaid soil in an amount from 0.1 to about 2 volumes of solution per porevolume of said soil.

6. The method of claim 1 wherein said polymer has from 7 to 65 percentof its amide groups hydrolyzed to carboxyl groups.

7. The method of claim 1 wherein the permeability of said soil isperiodically measured and the irrigation with said aqueous solution isperformed when the permeability of the soil is found to have increasedto an undersired level.

2. The method of claim 1 wherein said aqueous solution contains from0.001 to 1.0 weight percent of said polymer.
 3. The method of claim 2wherein said polymer has from 12 to 45 percent of its amide groupshydrolyzed to carboxyl groups.
 4. The method of claim 2 wherein saidtreating solution is applied to said soil in an amount from 0.05 toabout 5 volumes of solution per pore volume of said soil.
 5. The methodof claim 2 wherein said treating solution is applied to said soil in anamount from 0.1 to about 2 volumes of solution per pore volume of saidsoil.
 6. The method of claim 1 wherein said polymer has from 7 to 65percent of its amide groups hydrolyzed to carboxyl groups.
 7. The methodof claim 1 wherein the permeability of said soil is periodicallymeasured and the irrigation with said aqueous solution is performed whenthe permeability of the soil is found to have increased to an undersiredlevel.